Pistons with oil retaining cavities

Abstract

A piston has skirt portions (13) which are provided with parallel rows (14) of cavities (15) whose maximum depth below the surface of the skirt portion is 0.010 mm. Parts (20,23) of the skirt portion are left between the cavities for providing a reduced area, in comparison with the full skirt portion, for the transmission to an associated cylinder or liner of lateral loads; this reduced area reducing the frictional losses. The cavities (15) hold lubricating oil and provide a cushion of oil which supplies oil to the reduced bearing areas and which tends to resist lateral movement of the piston at top and bottom dead center, so reducing or eliminating "piston slap".

What is claimed is: 
     
       1. A piston for lubricated reciprocation in an internal combustion engine or a compressor comprising: a crown,   a gudgeon pin bore,   two skirt portions on opposite sides of said gudgeon pin bore,   a plurality of side-by-side rows of cavities which are formed in each said skirt portion and which are rectangular in shape with two shorter axially extending sides and two longer circumferentially extending sides interconnecting said shorter sides, adjacent cavities in a row having a common shorter side,   a land of generally rectangular shape formed by said skirt portions and extending circumferentially between adjacent rows of cavities for transmitting lateral loads from said piston to an associated cylinder, whereby the cavities hold lubricating oil for passage over said lands and for damping lateral movement of the piston.   
     
     
       2. A piston according to claim 1, wherein the cavities of each row are circumferentially staggered relative to the cavities of the or each next adjacent row. 
     
     
       3. A piston according to claim 2, characterized in that the rows of cavities of each skirt portion are symmetrically disposed about a plane including the piston axis and normal to the gudgeon pin bore axis. 
     
     
       4. A piston according to claim 1, wherein the rows of cavities of each skirt portion are symmetrically disposed about a plane including the piston axis and normal to the gudgeon pin bore axis. 
     
     
       5. A piston according to claim 1, wherein the base of each cavity is formed by two flat portions extending downwardly from respective shorter sides of the associated cavity and meeting at a base parallel to and intermediate said shorter sides. 
     
     
       6. A piston according to claim, 1 wherein the radial depth of each said base in between 0.005 and 0.015 mm. 
     
     
       7. A piston according to claim 1, wherein a plurality of rows of cavities are provided with the cavities of the rows relatively circumferentially staggered, each end of alternate rows of cavities terminating on a common edge lying on a plane including the piston axis, each end of the rows of cavities intermediate said alternate rows terminating before said edge, there being a further land between said termination of said intermediate rows and said edge. 
     
     
       8. A piston according to claim 1, wherein the skirt portion beyond said edges is radially relieved. 
     
     
       9. A piston for lubricated reciprocation in an internal combustion engine or a compressor comprising: a crown,   a gudgeon pin bore,   two skirt portions on opposite sides of said gudgeon pin bore,   a plurality of side-by-side rows of cavities which are formed on each said skirt portion and which are rectangular in shape with two shorter axially extending sides and two longer sides interconnecting said shorter sides, adjacent rows of cavities having common longer sides,   a land of generally rectangular shape extending axially between the shorter sides of adjacent cavities in each row for transmitting lateral loads from said piston to an associated cylinder, whereby the cavities hold lubricating oil for passage over said lands and for damping lateral movement of the piston.   
     
     
       10. A piston according to claim 9 wherein the cavities of each row are circumferentially staggered relative to the cavities of each next adjacent row. 
     
     
       11. A piston according to claim 9 wherein the rows of cavities of each skirt portion are symmetrically disposed about the plane including the piston axis and normal to the gudgeon pin bore axis. 
     
     
       12. A piston according to claim 9 wherein the base of each cavity is formed by two flat portions extending downwardly from respective shorter sides of the associated cavity meeting at a base parallel and intermediate said shorter sides. 
     
     
       13. A piston according to claim 9 wherein the radial depth of each said base is between 0.005 and 0.015 mm. 
     
     
       14. A piston according to claim 9 characterised in that said longer circumferentially extending sides interconnecting said shorter sides lie in respective planes inclined to planes normal to the piston axis, the planes of all the rows being mutually parallel.